Фазовая диаграмма системы Ge-Pr

Ge-Pr (Germanium-Praseodymium)
A.B. Gokhale, A. Munitz, and G.J. Abbaschian
The assessed Pr-Ge phase diagram is based primarily on [75Ere]. An error by [
75Ere] in construction in the peritectic reaction of Pr3Ge (800 C) has been
corrected. The melting temperatures of the pure components have been changed
to conform with the currently accepted values. [75Ere] mentioned that Ge does
not have an effect on the allotropic transformation temperature of Pr and
indicated a transformation temperature of 774 C, which is significantly
different from the currently accepted value of 795 C. This suggests that the
thermal arrest observed by [75Ere] at 774 C may be due to a catatectic
reaction involving (Pr). The reaction included in the assessed diagram
indicates that the presence of Ge depresses the allotropic transformation
temperature of Pr by 21 C.
PrGe2 has been included because [58Mat], [64Gla], [67May], [68Sam1], [69Rud1],
and [69Rud2] noted that it is isotypic with ThSi2. [67May] were able to
synthesize PrGe2 at 550 C by the amalgam method. [69Rud2] and [67Lyn]
indicated that PrGe2 is stable at the compositions 66.44 to 66.86 at.% Ge.
Although [75Ere] did not prepare an alloy in this range, they indicated that
PrGe2-x is isotypic with aGdSi2 at room temperature (the high-temperature form
is ThSi2 type). These compositions (66.44 and 66.86 at.% Ge) are outside the
composition limit given by [75Ere] for PrGe2-x. Because there are no
indications that PrGe2 undergoes an allotropic transformation, the data of [
75Ere] can be reconciled with the existence of PrGe2, if it is assumed that
PrGe2 decomposes peritectically near the polymorphic transformation
temperature of PrGe2-x. The thermal arrest observed by [75Ere] at 615 C may
be due to both a polymorphic transformation of PrGe2-x and a peritectoidal
decomposition of PrGe2, as shown in the assessed diagram. Because no other
information is available on the homogeneity range for PrGe2-x using the data
of [67Lyn] and [69Rud2], the range 66.44 to 66.86 at.% Ge is indicated in the
assessed diagram.
The solid solubility of Pr in (Ge) is less than 0.5 at.% at 700 C, and the
solid solubility of Ge in (Pr) is less than 2 at.% at the eutectic temperature
of 755 C [75Ere].
According to [68Sam2], [69Rud2], and [69Rud3], the character of the electrical
resistivity of Pr5Ge3, PrGe, and PrGe2 changes from metallic to semiconducting
type as a function of temperature at 526, 495, and 242 C, respectively. They
explained the transition in terms of changes in the electron energy states of
the intermediate phases.
According to [58Mat], PrGe2 is ferromagnetic, with a transition temperature of
19 K. [66Bus] determined that PrGe becomes ferromagnetically ordered on
cooling, with a magnetic transition temperature of 39 K. According to [67Bus],
Pr5Ge3 has a N‚el temperature (TN) of 12 K and an asymptotic Curie
temperature of 10 C.
58Mat: B.T. Matthias, E. Corenzwit, and W.H. Zachariasen, Phys. Rev., 112, 89 (
1958).
64Gla: E.I. Gladyshevskii, Zh. Strukt. Khim., 5, 568-575 (1964) in Russian; TR:
J. Struct. Chem., 5, 523-529 (1964).
66Bus: K.H.J. Buschow and J.F. Fast, Phys. Status Solidi, 16, 467-473 (1966).
66Hoh: D. Hohnke and E. Parthe, Acta Crystallogr., 20, 572-582 (1966).
67Bus: K.H.J. Buschow and J.F. Fast, Phys. Status Solidi, 21, 593-600 (1967).
67Lyn: K.A. Lynchak and T.Y. Kosolapova, Poroshk. Metall., (11), 92-96 (1967)
in Russian; TR: Sov. Powder Metall. Met. Ceram., 6(11), 923-926 (1967).
67May: I. Mayer, E. Yanir, and I. Shidlovsky, Inorg. Chem., 6(4), 842-844 (
1967).
68Sam1: G.V. Samsonov, Yu.B. Paderno, and B.M. Rud, Rev. Int. Hautes Temp.
R‚fract., 5(2), 105-110 (1968).
68Sam2: G.V. Samsonov, Yu.B. Paderno, and B.M. Rud, Izv. V.U.Z. Fiz., (7), 105-
107 (1968) in Russian; TR: Sov. Phys. J., (7), 71-72 (1968).
69Rud1: B.M. Rud and K.A. Lynchak, Poroshk. Metall., (7), 51-54 (1969) in
Russian; TR: Sov. Powder Metall. Met. Ceram., 8(7), 559-561 (1969).
69Rud2: B.M. Rud, K.A. Lynchak, and Yu.B. Paderno, Izv. Akad. Nauk SSSR, Neorg.
Mater., 5, 1350-1353 (1969) in Russian; TR: Inorg. Mater., 5, 1152-1155 (1969)
.
69Rud3: B.M. Rud, T.G. Kutsenok, and Yu.B. Paderno, Poroshk. Metall., (4), 34-
37 (1969) in Russian; TR: Sov. Powder Metall. Met. Ceram., 8(4), 284-287 (1969)
.
75Ere: V.N. Eremenko, Q.C. Xuong, Yu.I. Buyanov, and A.M. Kharkova, Izv. Akad.
Nauk SSSR, Neorg. Mater., 11, 160-162 (1975) in Russian; TR: Inorg. Mater., 11,
133-135 (1975).
Published in Bull. Alloy Phase Diagrams, 10(3) Jun 1989. Complete evaluation
contains 3 figures, 3 tables, and 25 references.
Special Points of the Pr-Ge System